Ben Dowell (eventually) finds out why Silent Witness star Emilia Fox took on the role of the brittle academic in Rapture, Blister, Burn at the Hampstead Theatre. When the play gets going that is...

Silent Witness star Emilia Fox took to the stage last night for the first time in ten years – was she right to do so?

She stars at the Hampstead Theatre as an attractive American academic called Catherine who breaks out of the seminar hall to return to her home town to look after her beloved Mom (Polly Adams), who has just had a heart attack.

Here she meets her old friends - Emma Fielding’s Gwen and Don (Adam James, pictured, above with Fox), a couple whose marriage is stultifying but who are jolted awake by her return. After all, Catherine was Don’s ex in their student days before roommate Gwen stole him away but now the tables are turned. Gwen is a recovering alcoholic who never finished her degree and Don is rotting away in an academic admin job. He's the traditional smart guy who never seems that interested in achieving anything and here has those classic traits of an addiction to porn and smoking pot.

Also rather predictably, Don’s passions are reignited; and when the affair starts with Catherine Gwen decides to swap lives with her rival to see how it goes in her New York apartment while Catherine shacks up with her husband, eating pizza, drinking a lot and trying out family life.

American stage and TV writer Gina Gionfriddo has a good pedigree, both as a writer (her Becky Shaw at the Almeida was excellent) and on the TV show Law & Order (among others).

But her latest play takes a while to get going. At first it feels far too abstracted, with the characters serving as mouthpieces for page after page of feminist theory. The summer classes Catherine takes with Gwen (before she flits) and her clever but frustrated babysitter Avery (Shannon Tarbet) just seems like an excuse to go over various ideas about a women’s place in the world, albeit on a very well-realised set representing Mom’s front room. But never mind the carefully studied details of an older America woman’s house (the sideboard, the cocktail shaker, the throws on the sofa), what this play needs (in its initial stages at least) is a bibliography.

But when Don and Catherine’s affair gets going, this becomes a properly dramatic piece of work and you can see why Fox took it on, ten years after she vowed to give up theatre for good after getting stinker reviews for her role in a West End revival of Les Liaisons Dangereuses.

Fox stops lecturing and presents a more human and rounded Catherine, whose tragedy is being so lonely and taken to family life that it means taking on a man like Don. Whether she can work through that... well you'll have to catch the play to find out.